Conventional IC package assemblies include components constructed from various materials with different coefficients of thermal expansion (CTE), including plastics, metals, and silicon. Where two components are connected by solder joints, a CTE mismatch between the two components can result in movement upon heating and cooling, which in turn produces a shear strain on the solder joints. Underfill is used in some IC package assemblies to reduce the CTE mismatch. Nonetheless, repeated thermal fluctuations can lead to fatigue fractures in the solder joints, underfill, and other components.